<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>封装ajax</title>
</head>
<body>
    
</body>
<script>
    function ajax(url){
        return new Promise((resolve,reject)=>{ 
            let xhr = new XMLHttpRequest();
            xhr.open('GET',url);//链接
            xhr.send();//发送资源
            xhr.onreadystatechange = function(){//监听状态
                console.log(xhr.readyState);
                if(xhr.readyState === 4){
                    if(xhr.status >= 200 && xhr.status < 300){
                        let res = JSON.parse(xhr.responseText);
                        resolve(res);
                    }else{
                        reject(xhr.responseText);
                    }
                }
            }
})}
            
    ajax('./01.json')
    .then(res=>{
        console.log(res);
    })
    .catch(err=>{
        console.log(err);
    })    



    
</script>
</html>